"Abby," Zenya Hernandez said, her voice breaking, "I want to say please come home. We miss you so badly. We want you back with us."

Local, state and federal agents continued to search for Abigail by land, water and air. Police have meticulously combed four square miles on land, scoured parts of the Saco River and paddled over Pudding Pond. The medical examiner was called twice to the scene on Saturday but neither time was related to Abigail's disappearance: One was for a hiker who died Saturday and another was after the discovery of human bone fragments from several years ago, police said.

Zenya Hernandez asked Abigail's friends to come forward with any information that could help return her safely, including whether there were recent changes in her behavior. She was mindful of the importance of the day: Abigail's 15th birthday.

"We love you and we miss you and happy birthday, Abby," she said.

Police are asking the public to remain vigilant. They've handed out posters with photos of the missing girl and have been stopping traffic to spread the word. Billboards carry Abigail's image and the number to call to report tips: 1-800-CALL-FBI.

The FBI is involved and enlisted the help of its Child Abduction Rapid Deployment Team, pulling in agents from as far away as Virginia to assist in the search.